The present invention relates to an apparatus for venting an annular space between a liner and the pipeline of a riser for conveying hydrocarbons.
Grooved liners are a technology used within steel pipelines as a cost efficient alternative to using Corrosion Resistant Alloys (CRA's) to construct pipelines transporting highly corrosive substances such as hydrocarbons. The system involves inserting a plastic liner, complete with a number of longitudinal external grooves, into the pipeline. The aim of the liner is to protect the carbon steel pipe from the highly corrosive nature of the production fluids. The grooves act as a method of transporting the gases/liquids that inevitably permeate through the liner to a venting location where they are released to atmosphere or stored in a collection vessel.
It is desirable to utilise the technology for vertical applications, such as production risers, Steel Catenery Risers (SCR) etc. Such applications involve lining vertical pipelines in exactly the same way as a standard horizontal pipeline. These vertical lines act as a method of transporting the production fluids from the main production transport line to the surface. In some applications, the production fluids are transported down to the seabed. Since some of these vertical lines can be exposed to depths in excess of 1000 m, a method of aiding flow to the surface is usually required. One such method is Gas Lift, in which processed gas is pumped cyclically through the system to push the fluids from the seabed to the surface.
In the vertical orientation, the liquid permeate will condense on the inner walls of the pipeline and fall to the base of the riser under gravity, where a column of liquid would quickly develop between the liner and the pipeline. This phenomenon dictates that a reliable venting system is required for the removal of the condensed permeate which collects at the base of the riser. This is necessary to avoid the situation where the liner experiences external overpressure and possible collapse in the event that there is a loss of internal pressure in the bore.